Referring to FIGS. 1A-1B, a system 100 is shown. The system 100 may be part of, or associated with, a turbo fan engine that utilizes a cascade type thrust reverser. There are typically a plurality of blocker doors 108 that deploy in order to redirect engine bypass air through a set of cascades 104 that turn the airflow out and forward in order to reverse the direction of the thrust of the engine. This may be done to slow an aircraft after landing.
The system 100 includes a sleeve 102 that is translated or moved in, e.g., an aft direction in order to deploy and expose cascades 104 of the thrust reverser. Similarly, in order to place the thrust reverser in a stowed state (e.g., during flight) the sleeve 102 is translated or moved in, e.g., a forward (FWD) direction, such that the sleeve 102 covers the cascades 104 and also may contact or abut a thrust reverser fixed structure 106 and form a seal therebetween to seal against any air leaking through the cascades.
While the radially outer surface of the fan duct 112 is defined mostly by the translating sleeve 102, the radially inner surface of the fan duct 112 is mostly defined by structure 114 typically termed the inner fixed structure (IFS) by those skilled in the art. The IFS 114 is typically fashioned in two halves which join together, one of the halves of a typical IFS is shown in FIG. 1B. The inside surface of the IFS 114 faces the engine core and helps define a chamber around the engine core to protect it. The outer surface of the IFS 114 faces the duct 112 and is smooth to minimize drag.
The system 100 includes a variable area fan nozzle (VAFN) 110. The VAFN 110 is translated forward or aft to control a nozzle area (denoted by arrow 116) associated with the duct 112. As is known to those of skill in this art, opening the VAFN 110 results in less back pressure on the bypass air fan (not shown) which is useful to protect against surge or other conditions potentially harmful to the fan.
Conceptually, or as part of a design philosophy, the VAFN 110 is typically an ‘add-on’ feature that adds weight and complexity to the propulsion system, but may also result in other offsetting benefits to the fan design. Accordingly, what is needed is a VAFN with overall better system efficiency and operational characteristics than previous VAFN designs.